To be honest the stats on the zeta in 3.0 content get pretty much obsolete by level 55-56ish but you can finish everything in the main story for the expansion with the zeta weapon without issue. I had my zeta until I replaced it with an upgrade law tomes weapon.

It was sad seeing a weapon that had that much time out into it just get tossed aside right away but that's the way the games fear progression is designed.

In terms of whether you should finish it or not, that's up to you and depending on where you are in the building process for the weapon it has gotten a lot easier to do with cheap materia prices increased alexandrite quantities, increased drop rates and the ability to Zerg most of the dungeons as an undersized party without the need to wait for duty finder, it's probably going to be a lot quicker to finish it than it was in 2.xx